Hurricane IRENE (Text)

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HURRICANE IRENE DISCUSSION NUMBER 12
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
500 AM EDT TUE AUG 23 2011
SMOOTHING THROUGH ALL OF THE AIRCRAFT FIXES SINCE IRENE MOVED OFF
THE COAST OF PUERTO RICO MORE THAN 18 HOURS AGO YIELDS A LONG TERM
MOTION OF 295/10 KT...WHICH IS USED FOR THIS ADVISORY. THERE IS NO
SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK REASONING. THE
23/00Z G-IV JET AIRCRAFT AND AIR FORCE C-130 DROPSONDE DATA APPEAR
TO HAVE SETTLED DOWN THE MODELS...AND THERE IS CONSIDERABLY LESS
DIFFERENCE AMONG THE VARIOUS MODEL SOLUTIONS NOW. THE OVERWHELMING
CONSENSUS IS THAT IRENE WILL GRADUALLY TURN NORTHWESTWARD OVER THE
NEXT 2-3 DAYS AND THEN MOVE NORTHWARD THROUGH A DEVELOPING BREAK IN
THE SUBTROPICAL RIDGE OVER THE SOUTHEASTERN UNITED STATES. THE
OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND
LIES VERY CLOSE TO CONSENSUS MODELS TVCN AND TVCA.
AN EARLIER RECON FLIGHT INDICATED THE PRESSURE HAD ONLY FALLEN BY 2
MB DOWN TO 978 MB...AND THE OVERALL APPEARANCE IN SATELLITE IMAGERY
HAS CHANGED LITTLE SINCE THE PREVIOUS ADVISORY. AS A RESULT...THE
INITIAL INTENSITY IS BEING HELD AT 85 KT...WHICH COULD BE GENEROUS.
IRENE IS FORECAST TO REMAIN IN A RELATIVELY LOW VERTICAL WIND SHEAR
ENVIRONMENT AND OVER SSTS NEAR 30C. THAT COMBINATION...ALONG WITH
EXPANDING OUTFLOW IN ALL QUADRANTS...SHOULD ALLOW FOR IRENE TO
BECOME A MAJOR HURRICANE WITHIN THE NEXT 24 HOURS ONCE THE CYCLONE
CLEARS THE EFFECTS OF HISPANIOLA...AND PROBABLY MAINTAIN MAJOR
HURRICANE STATUS THROUGHOUT THE REMAINDER OF THE 5-DAY FORECAST
PERIOD. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY
AND CLOSELY FOLLOWS A BLEND OF THE HWRF AND GFDL MODEL INTENSITY
FORECASTS...AND CONVERSION OF THE SURFACE PRESSURES DEPICTED IN THE
GFS AND ECMWF MODELS.
WIND RADII WERE EXPANDED BASED ON A BLEND OF RECON FLIGHT-LEVEL
WINDS...SFMR WINDS...AND SURFACE OBSERVATIONS.
IRENE IS FORECAST TO BECOME A LARGER THAN AVERAGE HURRICANE. IT IS
IMPORTANT TO REMIND USERS NOT TO FOCUS ON THE EXACT FORECAST
TRACK...ESPECIALLY AT DAYS 4 AND 5...SINCE THE MOST RECENT 5-YEAR
AVERAGE ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES...
RESPECTIVELY.
FORECAST POSITIONS AND MAX WINDS
INIT 23/0900Z 20.3N 70.1W 85 KT 100 MPH
12H 23/1800Z 20.9N 71.5W 95 KT 110 MPH
24H 24/0600Z 21.7N 73.3W 105 KT 120 MPH
36H 24/1800Z 22.9N 74.9W 110 KT 125 MPH
48H 25/0600Z 24.3N 76.2W 110 KT 125 MPH
72H 26/0600Z 28.0N 78.0W 115 KT 135 MPH
96H 27/0600Z 31.5N 78.3W 105 KT 120 MPH
120H 28/0600Z 35.0N 78.0W 100 KT 115 MPH...INLAND
$$
FORECASTER STEWART
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